1) Field of the Invention
The present invention relates to image processing apparatus and method, and a computer program product. More particularly, the present invention relates to the image processing apparatus, the image processing method, and the computer program product that are applied to a digital copying machine and a digital multifunction machine including a communication unit that performs data transmission and reception with an external device.
2) Description of the Related Art
An image processing apparatus of a digital color copying machine superposes four color toners of cyan, magenta, yellow, and black (CMYK) on one another to form a color image and a printer reproduces and outputs the color image. In such an image processing apparatus, a signal attribute of an image signal input from a scanner refers to red, green, and blue (RGB), and therefore, color correction and undercolor removal (UCR)-black generation are performed on the signal attribute to convert RGB to CMYK signals corresponding to the printer and toner characteristics, and the CMYK signals are output to the printer.
Most of the recent digital color copying machines have an image area separating function. The image area separating function is a function of identifying a black character, a color character, a dot-photograph portion, and a solid portion through image area separation. Therefore, this function is effective in acquisition of high-quality output image in a document with a plurality of image types mixed therein by performing appropriate image processing on each image area.
Reproduction of a high-quality black character in particular is demanded of color images. Consequently, the process of reproducing the black character identified through the image area separation with a black (K) single color becomes inevitable. This is because if the black character is reproduced with CMY(K), a colored portion is produced around the black character due to color misalignment that may occur on output by a printer, and this colored portion causes noticeable degradation in image quality. On the other hand, reproduction of the black character with the K single color is not affected by the color misalignment.
However, in the operation of the image area separation, there are two largely different types of processing for the black color in a black character portion and a photograph portion. More specifically, the K single color is used to reproduce the black character portion, while much of the CMY colors are used to reproduce the photograph portion for its gradation and graininess. These types of processing are switched based on a result of separation. Therefore, if the black character portion is failed to be identified properly, a boundary as the switched portion of the two types of processing may be sometimes visually recognized, which causes significant degradation in image quality. As explained above, identification with high accuracy is required for the image area separation.
In the recent tendency of the digital copying machines, a device as follows is known. In the device, an image signal input through a scanner is stored in a hard disk, and the image signal is once output by a printer, and then the same image signal can be output again by the printer without reading the same image signal through the scanner.
As explained above, there are various approaches to using the image signals stored in the hard disk, as follows. The image signal stored in the hard disk is transmitted or output to an external printer through an external interface. Alternatively, the image signal is transmitted to an external personal computer (PC), is edited by application software therein, and the edited image signal is returned again to the hard disk, and is output by the printer.
It is preferable that the signal attribute of the image signal stored in the hard disk is RGB or YCbCr. Because if the image signal with the image attribute of CMYK is stored, color characteristic and density characteristic are changed when the image signal is output by an external printer having different characteristic because CMYK are signals corresponding to the characteristics of the printer and toner. If the image signal with the image attribute of CMYK is stored in the PC, an image with the image signal cannot be viewed in many cases by general-purpose application software. Furthermore, if the image signal with the image attribute of CMYK is stored in the hard disk, memory is further taken up by one color. In addition, if calibration is performed during operation, then a desired color or density may not be output.
It is assumed that the image signal stored in the hard disk is RGB signals (data before the processing of UCR-black generation). For example, the image signal is subjected to processing by Joint Photographic Experts Group (JPEG) baseline compression technique (RGB is converted to YCbCr and is irreversibly compressed), and then the compressed image signal is stored in the hard disk. The compression is not limited to JPEG, but it is effective to use an irreversible compression format such as JPEG in order to make. effective use of memory space.
A case where the image area separation is executed by a signal before compression that is not affected by mosquito noise, block distortion, or degradation in sharpness is more excellent in identification accuracy. Therefore, the execution with the signal is effective in the image area separation that requires high identification accuracy. In order to use a black-character identification signal identified through the image area separation in the processing of UCR-black generation as a processing in a downstream stage of the compression, the black-character identification signal has to be brought into the downstream stage. Technologies to bring the black-character identification signal into the downstream stage are as follows. It is noted that Japanese Patent Application Laid Open (JP-A) Nos. Hei 4-10765 and Hei 5-308526 disclose image processing apparatuses with a first “method of storing an image-area identification signal in memory”, and JP-A No. Hei 8-98016 discloses an image processing apparatus with a second “method of merging an image-area identification signal in an image signal”.
The image processing apparatus disclosed in JP-A No. Hei 4-10765 reads a document and inputs image formation according to the document, compresses the image formation to be stored page by page, reads the stored image formation at a predetermined timing, and decompresses it to be output to a recording unit. This image processing apparatus includes an input unit that inputs image information, a compressor that irreversibly compresses the input image formation, and a storage unit that stores the compressed image formation. The image processing apparatus also includes a decompressor that decompresses the stored image formation, and a detector that detects edge information and color information based on the image formation after being input by the input unit but before being irreversibly compressed by the compressor and stores them. The image processing apparatus further includes a processor that performs processing so as to improve reproducibility on the image information that is read at the predetermined timing and decompressed, based on the stored edge information and color information. In other words, in the image processing apparatus disclosed in JP-A Hei 4-10765, in addition to the image signal, a black-character identification signal is also stored in memory, and both of them are brought into the downstream stage.
The image processing apparatus disclosed in JP-A No. Hei 5-308526 has a function of compressing an image signal that has been subjected to color separation and storing the compressed image signal. The image processing apparatus includes an attribute determining unit that determines an attribute of an image based on the image signal, a storage unit that stores a result of the determination, and a converter that converts the resolution as the result of the determination according to compression of the image signal. In other words, in the image processing apparatus disclosed in JP-A Hei 5-308526, the resolution of a black-character identification signal is converted to a reduced resolution to be stored in memory in order to economize on memory usage.
The image processing apparatus disclosed in JP-A No. Hei 8-98016 merges an image signal with a separation result. The image processing apparatus includes an image area separator that detects a black character area of an image, a separation-result merging unit that merges a result of separation with an image signal using a predetermined format, and a separation-result extracting unit that extracts the separation result from the image signal merged by the separation-result merging unit. The above-mentioned merger between the image signal and the separation result is performed by using the predetermined format such that the image is expressed by the image signal using a RGB color system, and the same values are set to an R signal, a G signal, and a B signal (R=G=B) for pixels indicating the black character area.
The demerits of the first “method of storing an image-area identification signal in memory” are such that the memory space is required more by an amount of a storage of the image-area identification signal. If the image-area identification signal is added to the image signal and they are transmitted to the external device from an external interface, a data amount is increased and versatility of the image signal is lost. Therefore, it is desirable to transmit only the image signal. However, if the image signal without the image-area identification signal is transmitted and is returned to hardware again through the external interface after the image is edited in PC, no corresponding separation result exists, and therefore there is no means to perform black character processing.
On the other hand, the merits of the first “method of storing an image-area identification signal in memory” are such that if the image-area identification signal is stored in a hard disk in an non-compression format or a reversible compression format, the image-area identification signal can be brought into the downstream stage without degradation in image quality. This allows improved accuracy of the image-area identification signal. These merits are opposite to the demerits from the viewpoint of the memory space. However, the image-area identification signal has not so many bits, and there is a unit for reducing the resolution for storage. Moreover, as hard disks are currently available at lower cost, an increase in memory capacity to be taken up by such an amount is not particularly a significant matter.
The demerits of the second “method of merging an image-area identification signal in an image signal” are such that if R=G=B pixels as black character code are embedded in the image signal and the black character code is extracted from the image signal, it is difficult to discriminate the black character code from the R=G=B pixels in a non-black character portion. If the non-black character portion is chromatized in advance or if the data used as the black character code is set to a lower pixel value that occurs at less frequency than that of the R=G=B pixels, it is possible to improve the identification accuracy. In any of the cases, the merged image signal is subjected to irreversible compression such as JPEG. Therefore, before and after the compression, the embedded black character code may be changed to a value that does not indicate the black character code, or the pixel that is not the black character code may be changed to the black character code. The merged image signal may also be affected by degradation due to variable magnification depending on a process flow.
The merits of the second “method of merging an image-area identification signal in an image signal” are such that as the image-area identification signal is merged in the image signal, the image signal can be transmitted to the external device without loss of versatility. In addition, the merged black character code can be held even in the image signal that is output to the external PC once and returned again to the hard disk.